DESCRIPTION This proposed study will continue a line of weight loss research that has been ongoing for seven years. The aim of the study is to compare the long-term weight losses achieved in a standard behavioral program with those obtained in an enhanced exercise intervention. The exercise goal in the standard program is 1000 kcal/week, while that in the enhanced exercise program is 2500 kcal/week. The study will be conducted with 180 subjects divided equally among men and women. Half will be recruited in Minneapolis and the other half in Pittsburgh. The primary hypotheses are that the enhanced exercise intervention group will have significantly greater weight losses than will the standard intervention group at the end of the 18 month treatment program and at the 30-month follow-up. In addition, the two conditions will be compared at 0, 6, 12, 18, and 30 months with regard to exercise level, variables that may be related to exercise and weight loss, and measures related to quality of life. Furthermore, the investigators will determine predictors of long-term weight loss and exercise behavior, and will examine the effect of social support on exercise level and weight loss of the enhanced exercise intervention group. Subjects will be randomized to the two conditions at each study center (Minneapolis and Pittsburgh). Both groups will receive the behavioral treatment program that includes group meetings, access to experienced therapists assisted by exercise physiologists, structured meal plans to help subjects reach individualized calorie goals, and training in the use of behavioral strategies to control food intake and increase physical exercise. The standard intervention will strongly encourage subjects to develop an exercise program based primarily on walking and bicycling. The enhanced exercise intervention will involve social support teams, individualized exercise prescriptions, shaping, injury prevention and management, feedback to participants about success in reaching their exercise goals, and financial incentives. Outcome measures will be obesity reflected in changes in weight, body composition, body fat distribution, and dual energy x-ray absorptiometry (DEXA), with the latter assessed only on subjects at the Pittsburgh Center,